1. Field of the Invention
This invention relates to an aqueous binder composition based on water-dispersible or water-soluble polyester resins containing sulfonate and hydroxyl groups and polyisocyanates and to a process for the production of a coating or sealing composition containing this aqueous binder composition.
2. Description of the Prior Art
By virtue of their outstanding properties, known two-component polyurethane coatings have acquired considerable significance in the coating field. However, a disadvantage is that their processing requires relatively large quantities of organic solvents which have to be eliminated, for example, by subsequent burning. In many applications, especially non-industrial applications, the organic solvents cannot be subsequently burned. Accordingly, high-solids coating compositions, preferably water-dilutable coating compositions are required for such applications in order to minimize solvent emission and the environmental pollution which it causes.
Normally, water cannot readily be used as the liquid phase of two-component polyurethane coating compositions containing free isocyanate groups because isocyanate groups react not only with alcoholic hydroxyl groups, but also with water to form urea and carbon dioxide. The pot life and quality of the coatings are thus generally reduced to levels which are unacceptable.
One possible solution is described in DE-OS 38 29 587 in which certain polyhydroxypolyacrylates are combined with polyisocyanates containing free isocyanate groups to form water-containing two-component systems.
It has now surprisingly been found that water-containing polyester resins containing sulfonate and hydroxyl groups can also be used with polyisocyanates containing free isocyanate groups in water-based two-component binders.